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clean up mips (32-bit, o32) syscall asm constraints

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analogous to commit ddc7c4f936 for
mips64 and n32, remove the hack to load the syscall number into $2 via
asm, and use a constraint to let the compiler load it instead.

now, only $4, $5, and $6 are potential input-only registers. $2 is
always input and output, and $7 is both when it's an argument,
otherwise output-only. previously, $7 was treated as an input (with a
"1" constraint matching its output position) even when it was not an
input, which was arguably undefined behavior (asm input from
indeterminate value). this is corrected.

as before, $8, $9, and $10 are conditionally input-output registers
for 5-, 6-, and 7-argument syscalls. their role in input is carrying
in the values that will be stored on the stack for arguments 5-7.
their role in output is carrying back whatever the kernel has
clobbered them with, so that the compiler cannot assume they still
contain the input values.
This commit is contained in:
Rich Felker 2019-09-27 09:57:54 -04:00
parent 12fecbb4ec
commit 604f8d3d8b
1 changed files with 32 additions and 31 deletions
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63
arch/mips/syscall_arch.h
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@ -18,10 +18,11 @@
static inline long __syscall0(long n)
{
register long r7 __asm__("$7");
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"addu $2,$0,%2 ; syscall"
: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7)
"syscall"
: "+r"(r2), "=r"(r7)
:
: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
return r7 ? -r2 : r2;
}
@ -30,11 +31,11 @@ static inline long __syscall1(long n, long a)
{
register long r4 __asm__("$4") = a;
register long r7 __asm__("$7");
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"addu $2,$0,%2 ; syscall"
: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
"r"(r4)
"syscall"
: "+r"(r2), "=r"(r7)
: "r"(r4)
: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
return r7 ? -r2 : r2;
}
@ -44,11 +45,11 @@ static inline long __syscall2(long n, long a, long b)
register long r4 __asm__("$4") = a;
register long r5 __asm__("$5") = b;
register long r7 __asm__("$7");
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"addu $2,$0,%2 ; syscall"
: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
"r"(r4), "r"(r5)
"syscall"
: "+r"(r2), "=r"(r7)
: "r"(r4), "r"(r5)
: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
return r7 ? -r2 : r2;
}
@ -59,11 +60,11 @@ static inline long __syscall3(long n, long a, long b, long c)
register long r5 __asm__("$5") = b;
register long r6 __asm__("$6") = c;
register long r7 __asm__("$7");
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"addu $2,$0,%2 ; syscall"
: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
"r"(r4), "r"(r5), "r"(r6)
"syscall"
: "+r"(r2), "=r"(r7)
: "r"(r4), "r"(r5), "r"(r6)
: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
return r7 ? -r2 : r2;
}
@ -74,11 +75,11 @@ static inline long __syscall4(long n, long a, long b, long c, long d)
register long r5 __asm__("$5") = b;
register long r6 __asm__("$6") = c;
register long r7 __asm__("$7") = d;
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"addu $2,$0,%2 ; syscall"
: "=&r"(r2), "=r"(r7) : "ir"(n), "0"(r2), "1"(r7),
"r"(r4), "r"(r5), "r"(r6)
"syscall"
: "+r"(r2), "+r"(r7)
: "r"(r4), "r"(r5), "r"(r6)
: SYSCALL_CLOBBERLIST, "$8", "$9", "$10");
return r7 ? -r2 : r2;
}
@ -90,13 +91,13 @@ static inline long __syscall5(long n, long a, long b, long c, long d, long e)
register long r6 __asm__("$6") = c;
register long r7 __asm__("$7") = d;
register long r8 __asm__("$8") = e;
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"subu $sp,$sp,32 ; sw $8,16($sp) ; "
"addu $2,$0,%3 ; syscall ;"
"syscall ;"
"addu $sp,$sp,32"
: "=&r"(r2), "=r"(r7), "+r"(r8)
: "ir"(n), "0"(r2), "1"(r7), "r"(r4), "r"(r5), "r"(r6)
: "+r"(r2), "+r"(r7), "+r"(r8)
: "r"(r4), "r"(r5), "r"(r6)
: SYSCALL_CLOBBERLIST, "$9", "$10");
return r7 ? -r2 : r2;
}
@ -109,13 +110,13 @@ static inline long __syscall6(long n, long a, long b, long c, long d, long e, lo
register long r7 __asm__("$7") = d;
register long r8 __asm__("$8") = e;
register long r9 __asm__("$9") = f;
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"subu $sp,$sp,32 ; sw $8,16($sp) ; sw $9,20($sp) ; "
"addu $2,$0,%4 ; syscall ;"
"syscall ;"
"addu $sp,$sp,32"
: "=&r"(r2), "=r"(r7), "+r"(r8), "+r"(r9)
: "ir"(n), "0"(r2), "1"(r7), "r"(r4), "r"(r5), "r"(r6)
: "+r"(r2), "+r"(r7), "+r"(r8), "+r"(r9)
: "r"(r4), "r"(r5), "r"(r6)
: SYSCALL_CLOBBERLIST, "$10");
return r7 ? -r2 : r2;
}
@ -129,13 +130,13 @@ static inline long __syscall7(long n, long a, long b, long c, long d, long e, lo
register long r8 __asm__("$8") = e;
register long r9 __asm__("$9") = f;
register long r10 __asm__("$10") = g;
register long r2 __asm__("$2");
register long r2 __asm__("$2") = n;
__asm__ __volatile__ (
"subu $sp,$sp,32 ; sw $8,16($sp) ; sw $9,20($sp) ; sw $10,24($sp) ; "
"addu $2,$0,%5 ; syscall ;"
"syscall ;"
"addu $sp,$sp,32"
: "=&r"(r2), "=r"(r7), "+r"(r8), "+r"(r9), "+r"(r10)
: "ir"(n), "0"(r2), "1"(r7), "r"(r4), "r"(r5), "r"(r6)
: "+r"(r2), "+r"(r7), "+r"(r8), "+r"(r9), "+r"(r10)
: "r"(r4), "r"(r5), "r"(r6)
: SYSCALL_CLOBBERLIST);
return r7 ? -r2 : r2;
}